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Rheologische Untersuchungen zum Einfluss des TBPMN-Netzwerkes auf die scherinduzierte Kristallisation von Polypropylen
Get PDFDie gedruckte Fassung der Dissertation erschienen im Universitätsverlag der TU Berlin unter der ISBN 978-3-7983-2642-2.Kunststofferzeugnisse aus Polypropylen besitzen auf Grund der großen Produkt- und Eigenschaftsvielfalt einen enormen Verbreitungsgrad. Als teilkristalliner Thermoplast zeichnet sich isotaktisches Polypropylen (iPP) zudem durch zwei dominierende Kristallmodifikationen (α-iPP und β-iPP) mit unterschiedlichen Strukturen und Eigenschaften aus. Die Verarbeitungsverfahren erstrecken sich vom Spritzgießen über das Blasformen bis hin zum Tiefziehen und Schweißen. Dabei wird der Kunststoff einer großen Scherdeformation unterworfen, die einen prägenden Einfluss auf die Mikrostruktur und auf die makroskopischen Eigenschaften hat. Eine gleichzeitig zur Abkühlung einwirkende Scherdeformation kann die Kristallisation beschleunigen und Gefügeorientierungen hervorrufen. Der Einsatz und die stetige Verbesserung von Sorbitol-Derivaten als Nukleierungsmittel in iPP ist von hoher technischer und wirtschaftlicher Bedeutung. Mit ihrer Verwendung wird eine Gefügeverbesserung sowie eine gezielte Beeinflussung der mechanischen und optischen Eigenschaften angestrebt.
Ziel dieser Arbeit ist es, für isotaktisches Polypropylen (α-iPP) das Phasenverhalten und die Nukleierungswirkung der aktuellen Sorbitol-Entwicklung 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)-methylen]-nonitol (TBPMN) eingehend thermodynamisch, rheologisch und röntgenographisch zu charakterisieren.
Im Ergebnis konnten thermodynamische und linear-viskoelastische Untersuchungen zur TBPMN-Ausscheidungsdynamik eine graduelle Zunahme der Umwandlungstemperaturen mit steigendem TBPMN-Anteil nachweisen. Ein Optimum von Kristallinität und von Nukleierungseffizenz wird schon bei geringem TBPMN-Gehalt erzielt und eine weitere Konzentrationserhöhung ermöglicht lediglich eine minimale Steigerung der Nukleierungswirkung. Die iPP/TBPMN-Systeme zeichnen sich im Zustand der homogenen Schmelze durch ein identisches linear-viskoelastisches Verhalten aus. Erst bei Erreichen der konzentrationsspezifischen Ausscheidungstemperaturen tritt thermorheologisch komplexes Verhalten auf. Die Fibrillen-Struktur des TBPMNs zeigt sich im van Gurp-Palmen-Plot durch Minima der Gelsteifigkeit.
Schon geringe TBPMN-Konzentrationen bewirken eine signifikante Beschleunigung der Kristallisation. Bei Scherdeformationen mit konstanter Scherrate lässt sich für alle nukleierten Systeme ein exponentieller Zusammenhang von Induktionszeit und Scherrate feststellen. Dabei kann durch die Berechnung der Weissenberg-Zahlen für nicht-modifiziertes iPP ein molekularer Bezug für den Übergang von punktförmigen Keimen zu orientieren Kettensegmenten hergestellt werden. Im Gegensatz zu der geringen Konzentrationsabhängigkeit bei Scherung mit konstanter Scherrate führt eine kurzzeitige Scherung zu einer TBPMN-Abhängigkeit mit Potenzcharakter. Die Induktionszeitabnahme erfolgt reziprok proportional zur Nukleierungsmitteloberfläche, so dass die Annahme eines epitaktischen Aufwachsens von iPP auf TBPMN-Fibrillen bestätigt wird.
Durch Ex-situ-Weitwinkel-Röntgenbeugung (WAXD) wird eine deutliche Texturbildung in Abhängigkeit vom rheologischen Deformationsprofil nachgewiesen. Eine detaillierte Analyse der kristallographischen Verzweigungsbildung von iPP zeigt, dass diese unabhängig vom Nukleierungsmittel TBPMN und ausschließlich deformationsbestimmt erfolgt.The properties of plastics are strongly influenced by the method of manufacture, processing conditions and microstructure. Hence, polymer crystallization has attracted great scientific and industrial attention during the past 30 years. Isotactic polypropylene (iPP) is a commonly used semi-crystalline thermoplastic with exceptional mechanical properties. Since the α-phase of iPP is the thermodynamically stable crystalline form, it is the most common modification of iPP. Current investigations concerning crystallization kinetics of polypropylene have led to the development of a vast variety of novel nucleating agents. The use of organic nucleators, for example sorbitol derivates, facilitates increased efficiencies of nucleation, because polymer chains epitaxially crystallize at these finely dispersed sugar networks.
The present study aimed to investigate the crystallization kinetics and the nucleation efficiency of iPP blended with the novel sorbitol derivate 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)-methylene]-nonitol (TBPMN). Special emphasis was given to iPP/TBPMN phase behaviour and to the effect of shear deformation on the microstructure formation. A standard isotactic polypropylene with narrow MWD was blended by extrusion with various concentrations of TBPMN.
Dynamic DSC analysis of nucleated iPP at quiescent conditions verified a general improvement of crystallinity and nucleation efficiency. Furthermore, reaction of iPP with TBPMN was analysed by dynamic DSC experiments in order to evaluate phase behaviour and miscibility. The thermal stability of TBPMN was
evaluated by TGA measurements in oxygen and nitrogen atmosphere. Finally the degradation products of the nucleating agent were characterized by means of FTIR spectroscopy.
Crystallization kinetics of iPP under shear treatment were dominated by TBPMN and its network formation during liquid-solid phase separation. Oscillative temperature sweeps within the linear viscoelastic regime allowed a characterization of gelation and temperature hysteresis. An optimum in the nucleation efficiency was reached at small concentrations of TBPMN although larger amounts of sorbitol led to an increase in transition temperatures. Furthermore, phase separation effects and their influence on flow induced crystallization (FIC) were analyzed by linear oscillative shear rheology at different temperature histories related to TBPMN transition temperatures. Prior to TBPMN phase separation from the homogeneous melt, all nucleated systems showed the same linear viscoelastic characteristics as non-modified iPP. But at the starting point of liquid-solid phase separation, a change in the viscoelastic response to thermorheological complexity was detected.
In order to investigate the formation of flow orientated iPP crystals, various deformation histories were imposed on the TBPMN network prior to polypropylene crystallization. Step-shear and continuous-shear experiments were performed in order to study the dominating effects on flow induced crystallization kinetics such as shear rate or shear time. Continuous shear histories with constant shear rate resulted in an exponential relation between induction times and shear rate. Based on the determination of Weissenberg numbers (We) for non-modified iPP, a correlation of the transition from point-like nuclei to oriented structures was obtained. In contrast to deformations with constant shear rate, step-shear experiments revealed a power law dependency between TBPMN content and induction times. The power law exponent obtained from the experimental data indicates an epitaxial growth of polypropylene chains on TBPMN fibrilla.
WAXD analysis of reflections of the iPP α-crystals showed a strong alignment of the polymer chains due to FIC as well as a shear deformation dependency of crystallographic branching, especially for step-shear histories
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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